Update git submodules

Update git submodules

* Update docs/submodules/releng-xci from branch 'master'
  - Merge "Export OPENSTACK_REQUIREMENTS_VERSION"
  - Export OPENSTACK_REQUIREMENTS_VERSION

    The hash value for the OpenStack requirements project is consumed
    for other projects which can be out of the openstack-ansible scope.
    This change creates the OPENSTACK_REQUIREMENTS_VERSION variable using
    the openstack_services.yml value as default one.

    Change-Id: I4544bcc3f14c107aab8ebba1dced1ba203f07f68
    Signed-off-by: Victor Morales <victor.morales@intel.com>